Powder feed device for flame spray guns



March 17, 1970 I H. S.-DALEY 3,501,097

POWDER DEVICE FOR FLAME SPRAY GUNS Filed Dec. 29, 1966 Sheets-Sheet 1 I 4 l 3 16 v I 17 46 l I8 IO -1 A 22 21 I2 3 l 49 |I3 52 26 45 M I l I n 24 29 -42 v'. if 40- 35\ afa so 5! =5: 34 i ii I INVENTOR HORACE S. DAL EY ATTORNEYS.

March 17, 1970 H. s DALEY 3,501,097

POWDER FEED DEVICE FOR FLAME SPRAY GUNS Filed Dec. 29, 1966 s Sheets-Sheet 2 23 20 O I I I' I I 4 INVENTQR HORACE s. DALEY ATTORNEYS.

I March 17, 1970 H. 8-. DALEY Filed Dec. 29, 1966 POWDER DEVICE FOR FLAME SPRAY GUNS 3 Sheets-Sheet 5 32 62 MOTOR 5: 63

33- PRESET L 39 PRESSURE w 40 REGULATOR -T so 51 5 INVENTOR HORACE s. DALEY ATTORNEYS.

United States Patent 3,501,097 POWDER FEED DEVICE FOR FLAME SPRAY GUNS Horace S. Daley, Clifton, N.J., assignor to Metco Inc., Westbury, N .Y. Filed Dec. 29, 1966, Ser. No. 605,647 Int. Cl. F23k 1/02 US. Cl. 239-85 16 Claims ABSTRACT OF THE DISCLOSURE An apparatus for feeding powder at a controlled rate to a flame spray gun having an enclosed supply hopper which gravity-feeds powder to a rotating bucket wheel which conveys the powder into a carrier gas flowing at a constant rate for entrainment and transportation to the flame spray gun. The pressure drop along the feed line past the point of powder introduction is utilized to indicate the powder flow rate and/or control the same. The powder being conveyed is passed through a conically narrowing accumulating chamber in which a certain amount of powder deposits out and is maintained, the quantity of powder being enor detrained varying the average cross section of the chamber and thus the flow velocity therethrough to automatically maintain a uniform powder feed.

BACKGROUND OF THE INVENTION Flame spraying involves the heat-softening or melting of a heat-fusible material, such as metal or ceramic and the propelling or spraying of the softened material against the surface to be coated. Flame spraying is effected utilizing a flame spray gun. In certain types of guns the heatfusible material is initially fed through the gun in powdered form. Guns which are so supplied with material to be sprayed in powdered form are known as powder-type flame spray guns. The powdered material is generally known as a flame spray powder and is usually of a relatively small particle size, as for example below about 140 mesh US. Standard screen size. The flame spray guns utilize a combustion or plasma flame and in many guns the powder is fed to the gun or into the guns flame entrained in a carrier gas. In order to obtain high quality coatings it is necessary to accurately control the rate of 4 powder fed through the gun and to maintain the same constant for given spray conditions. Powder, and particulary fine powder of the type used as flame spray powder has proven to be a diflicult material to handle and feed in a carrier gas at the desired uniform rate. While various apparatuses of different designs and modes of operation utilizing gravity, mechanical and gas conveyances and combinations thereof have been proposed, these devices almost universally suffer from a lack of reliability in maintaining a constant controlled powder feed and are quite often subject to mechanical wear and breakdown caused by the powder. Furthermore, difliculties have been encountered in determining the actual amount of powder fed to the stream, heretofore it has not been while it is possible to accurately measure the rate of flow of the gas stream itself and to measure the amount of powder fed to the stream, heretofore, it has not been possible to accurately and instantaneously measure the amount of powder actually being conveyed in the carrier gas stream.

One object of this invention is a powder feed device for a flame spray gun which will reliably feed powder at a controlled rate without the above mentioned disadvantages.

A further object of this invention is an indicator arrangement for a flame spray powder feeder which will continuously provide an indication reading of the amount of powder actually being conveyed to the gun.

A further object of this invention is a control system for controlling the powder flow rate of a flame spray powder feeder which operates on a feed-back principle.

A still further object of this invention is an accumulator arrangement for a flame spray powder feeder which automatically will maintain a uniform quantity of powder in a carrier gas under given conditions.

These and still further objects will become apparent from the following description read in conjunction with the drawings.

SUMMARY OF THE INVENTION The powder feeder in accordance with the invention is provided with a gravity flow passage which is fed by gravity flow from a supply hopper maintained above it. A bucket wheel arrangement picks powder up from this gravity feed passage and conveys the same into a mixing chamber through which a carrier is flowed at a constant flow rate, the carrier gas picking up and entraining the powder and conveying the same through a conduit or tube to the flame spray gun. The bucket wheel is loosely fitted and rotates in a chamber with a portion of its periphery extending into the gravity feed passage and another portion of its periphery, angularly displaced from the first portion in the direction of rotation, extending in the mixing chamber.

The angle between the highest point of intersection between the gravity feed passage and the bucket wheel chamber and the lowest point of intersection between the bucket wheel chamber and the mixing passage is less than the natural angle of repose of powdered material to be fed through the device, as for example less than 350, so that powder cannot by gravity flow from the gravity feed passage to the mixing passage and must be mechanically conveyed by the bucket wheel which may thus be loosely positioned without any close tolerances or seals which could cause wear and jamming. Preferably passages are provided to maintain an equalized pressure throughout the system and thus to prevent pressure differentials or surges from effecting the powder feed. The hopper system is preferably provided with an automatic valving arrangement which allows removal without powder spillage or loss and is most preferably provided with a double chamber and a valving arrangement which allow opening and filling of the upper chamber without interruption of operation in spite of the maintaining of the pressure equalization.

The powder passage or conduit down stream of the point of powder introduction into the carrier gas is pro vided with an accumulator chamber of a progressively decreasing flow cross section in the down stream direction in which a certain amount of powder accumulates, the amount of accumulating powder controlling the average cross section and thus the flow velocity acting as a feed self-equalizer under given operating conditions. This accumulator arrangement is applicable to powder feed devices in general in which the powder is entrained in a carrier gas.

I have furthermore surprisingly discovered that as a relatively small amount of powder is introduced into a carrier gas flowing through a conduit at a constant rate, a significant increase in the pressure drop along any given segment or the entire length of the conduit occurs, which pressure drop varies as a function of the amount of powder being actually conveyed in the carrier gas.

In accordance with the invention this pressure drop is measured by a pressure-sensitive instrument, such as a pressure gauge in order to determine the powder flow rate and changes thereof. In accordance with a further embodiment of the invention this change in the pressure drop is utilized to automatically control the powder feed.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a vertical section of an embodiment of a powder feeder in accordance with the invention;

FIG. 2 is a partial vertical section of the device shown in FIG. 1;

FIG. 3 is a perspective view of an embodiment of the invention;

FIG. 4 is a perspective exploded view showing in detail the bucket wheel arrangement and housing block containing the bucket wheel chamber of the embodiment shown in the previous figures;

FIG. 5 is a perspective view showing the feed hopper with its foot valve arrangement as removed from the device of FIGS. 1, 2 and 3;

FIG. 6 is a perspective view of the bottom plug member of the hopper reservoir of the embodiment shown in the previous figures;

FIG. 7 diagrammatically shows the feeder of the previous figures with an embodiment of an automatic control arrangement in accordance with the invention;

FIG. 8 diagrammatically shows a further embodiment of a powder feeder utilizing the control regulation principle in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In the embodiment as shown in FIGS. 1 through 6, 1 represents a hopper reservoir which is provided with the cover plate 2 having the O-ring pressure seal 3. A hollow tubular tie rod 4 is secured to the cover plate 2 by means of the spider arrangement 5 and nut 6. A filling plug 7 is removably secured to the tie rod 4 by means of the thread connection 8 and is pressure sealed in position by means of the O-ring seal 9. The tie rod 4 is secured at its lower end to the bottom plug 10. The bottom plug 10 is conically tapered at its upper end which extends in the reservoir hopper 1 and is provided with four equally spaced powder feed passages 11 of circular cross section. The powder feed passages 11 converge into a central powder outlet 12 of circular cross section which forms a valve seat for the powder valve 13. The powder valve 13 is connected to the lower end of the valve rod 14, which extends concentrically through the tubular tie rod 4, projecting out of the upper end thereof at 15. A spring 16 resiliently urges the valve rod 14 upwardly toward a position shutting the powder valve 13 against the seat formed at 12, thus sealing the reservoir hopper 1. When the filling plug 7 is, however, screwed in place it contacts the upper end 15 of the valve rod forcing the same downwardly compressing the spring 16 and opening the valve 13. The bottom plug 10 is furthermore provided with gas flow passages 17 and 18 which communicate the central opening 12 with the interior of the tubular tie rod 4. The tubular tie rod 4 has the lateral gas bleed holes 19 at its upper end so that there is a gas flow communication from the central opening 12 through the passages 18 and 17 up through the tubular tie rod 4 through the lateral openings 19 to the upper portion of the reservoir hopper 1. The reservoir hopper 1 is secured in axial alignment above the powder feed hopper 20 and the entire unit is secured to the housing of the device by means of the screw flange 21 which secures the reservoir hopper 1 and the feed hopper 20 together and holds the hopper 20 in the holding bracket 23 of the housing. A pressure-tight seal is achieved between the reservoir hopper 1 and hopper 20 by means of the O-ring seal 22. The lower end of the hopper 20 is conically tapered at 24 and a rod 25 extends axially through the feed hopper 20 and has the valve foot member 26 connected at its lower end. The rod 25 is secured in position for axial movement by means of the spider arrangement 27 and is biased by the spring 28 so that the O-ring 29 on the valve foot will tend to be sealed in contact with the inner conical surface of the hopper at 24. The upper end of the rod 25 slidably extends into a cylindrical socket in the lower end of the powder valve 13. The rod 25 is hollow and the valve foot 26 has a central bore 30 extending as a continuation of the hollow interior thereof.

The lower end of the portion 24 of the hopper 20 extends into a cylindrical bore 31 in the housing block 32 which may, for example, be constructed of plastic, such as Lucite. The valve foot 26 by contact with a shoulder in the bore 31 is held in an upward position with the spring 28 compressed. A powder flow passage is thus provided around the seal 29 into the powder feed chamber 33, which preferably has a slight reverse taper. A pressure seal is formed by an O-ring which extends around the tip of the portion 24. The powder feed chamber extends downwardly to the lower end of the block 32 and is sealed to its lower end by the clean-out plug 34. A cylindrical bucket wheel chamber 35 is cut in the block 32 and intersects the feed chamber 33. A bucket wheel 36 is rotatably mounted in the chamber 35 and has the construction as shown in FIG. 4, being provided with the bucket sections 37. The upper edge 38 where the feed chamber intersects the bucket wheel chamber 35 is preferably above a horizontal line extending through the axis of rotation of the bucket wheel. The upper edge 38 should preferably be somewhat below a point adjacent to a point on the bucket wheel where a tangent to the bucket wheel forms an angle with the horizontal equal to the angle of repose of the powder. Most preferably this point of intersection 38 should be below this highest point by an amount not exceeding 20 as measured from the axis of the bucket wheel. A mixing passage 39 extends vertically through the block 32 on the opposite side of the bucket wheel chamber 35 and intersects the bucket wheel chamber so that the lower edge of the intersection 40 is so positioned that a line drawn between this point and the point 38 has an angle of inclination less than the natural angle of repose of powder to be treated and preferably, for example, an angle of less than about 35 of the horizontal. A connection to the carrier gas line (not shown) leads into the rear of block 32 at 41, and a gas nozzle 42 is secured in the mixing passage 39 so that gas passed through the passage 41 will pass into the passage 39 through the lateral feed holds 43 and down through the central passage 44 of the nozzle. A small amount of gas will flow as a cleaning sheath around the outside of the nozzle due to a slight tolerance in the fit. An equalizer tube 45 is connected to the passage 41 before it leads into the mixing chamber 39 by means of a T connection. The equalizer tube 45 leads to a lateral connection 46 in the body which, in turn leads into a passage 47 and an equalizing gas tube 48 which is provided with an outlet at its lower end and a lateral outlet 49 at its upper end. Due to this connection of the equalizer tube and due to the bore 30, hollow interior of the rod 25, and further due to passages 17, 18, the hollow interior of the tie rod 4 and passage 19, the pressure throughout the system as thus far described remains the same as the pressure of the carrier gas. To further aid in this function, an inclined equalizer passage 49a extends in the block 32 connecting the upper portion of the cutout 40 in pressure communication with the top of the feed chamber 33.

The mixing passage 39 extends into a conically tapered accumulator passage 50 which in turn leads to the c0nnection 51 which is connected to the feed line or conduit of the flame spray gun, as for example a plasma flame spray gun. A pressure gauge 52, as for example, a conventional diaphragm-type pressure gauge is connected by a further T connection to the inlet passage 41. This pressure gauge will thus indicate changes in the pressure drop along the powder conduit past the point of powder introduction and thus the powder feed rate, as hereinafter described in further detail. The bucket wheel 36 is driven by the electric motor 53 through the conventional gear drive, as shown in FIG. 2. The motor is an adjustable speed motor the speed of which is controlled by a control knob 54 in the conventional manner. Preferably the motor 53 is an armature voltage controlled D.C. motor using a silicon controlled rectifier (SCR) in which the back EMF is used to govern the motor speed.

In operation with the hoppers 1 and.20 loaded with powder to be sprayed a carrier gas is caused to flow through the device at a constant flow rate as controlled by conventional flow meter 55 (FIG. 3). The flow, as for example, in cubic feet per hour being maintained steady throughout the operation. Powder due to gravity will fill the feed chamber 33, but even in absence of any mechanical seal around the bucket wheel 33 cannot pass through the bucket wheel chamber 35 into the mixing chamber 39 due to the fact that the natural angle of repose of the powder will not bring it to above point 40. This allows a positioning of the bucket wheel with very wide tolerances and with no mechanical seal (save for shaft which extends into the motor) and thus avoids the danger of clogging and jamming with powder.

As the bucket wheel 36 is rotated at a controlled speed as controlled by the control knob 54 and motor 53, the powder is picked up in the buckets of 37 and dumped into passage 39 at a rate which is solely controlled by the speed of rotation of the bucket wheel. Due to the fact that the edge 38 is above the axis of rotation of the bucket wheel, the feed in the chamber 33 to the bucket wheel is always a positive direct vertical gravity feed which does not depend on any lateral transfer or flow. The reverse conical tapering ensures that the passage is always kept full of powder in the area where the buckets 37 pick the same up and voids and bridging are prevented. The equalization passage 49 and other pressure equalization features ensure that pressure differential factors would not affect the powder flow or feed. The carrier gas flowing through the passage 41 and out through the outlet 44 picks up and entrains powder in the mixing passage 39, passing the same through the accumulator chamber 50 out through the connection 51 through the feed conduit or hose to the flame spray gun.

The amount of powder which may remain entrained in the gas stream varies directly with the flow velocity. A certain quantity of powder will accumulate in the accumulator passage 50. Due to the conical narrowing of the accumulator passage 50 the gas velocity progressively increases as the same flows therethrough. If, for example, a greater amount of powder is dropped out of the gas into the accumulator chamber 50, it will fill the accumulator chamber along a greater degree of its length and thus the powder will be in contact with gasmoving at higher velocity and a greater amount of powder will thus be picked up. Conversely if a greater amount of powder is picked up by the gas, the powder remaining in the accumulator chamber will only extend along a lesser degree of length of the chamber and thus the powder will be in contact with gas flowing at a lower velocity which will not pick up the powder as with the gas flowing at a higher velocity. Furthermore, the filling of the passage to a greater and lesser extent will vary the average cross-sectional size of the chamber and thus the average velocity of the gas passing therethrough. With a greater degree of filling the average velocity will increase and more powder will be picked up and with a lesser degree of powder the average velocity will decrease and more powder will tend to drop out of the gas. Section 50 thus acts as an automatic equalization control, and furthermore compensates for any tendency toward a pulsed or intermittent powder feed as is inherent in a bucket wheel system. This principle of operation of the equalizer chamber may be utilized in connection with any powder feed system in which powder is entrained in a carrier gas. Any chamber for accumulating powder from the gas stream which is horizontally positioned, has an enlarged cross-sectional inlet, and reduced cross-sectional outlet may be used. The term horizontally as used herein and in the claims is intended to designate a chamher the lower surface of which extends in a general horizontal direction and which is not inclined downwardly at an angle sufficient to cause gravity fiow of powder thereon.

If the powder feed rate increases so that a greater amount of powder is conveyed through theconduit, the pressure drop along the conduit past the point of introduction will substantially increase and this increase is shown on the gauge 52. By adjusting the control 54 so that the reading on the gauge 52 which may be in any arbitrary units, remains constant, the powder feed rate will also be so retained at a constant value. These varia tions in the pressure are equalized throughout the system by pressure communication through the equalizer tube 45, connection 46 and tube 48 by the passage 17, 18, the hollow interior of the tube 4 and the lateral passages 19. This equalization prevents pressure differential factors in the system from affecting the powder feed.

If the supply of powder in the reservoir hopper 1 becomes low, it is possible to refill this hopper during operation without interruption. For this purpose the filling plug 7 is unscrewed from the cover plate 2. As this filling plug is unscrewed the spring 16 will force the rod 14 upwardly closing the powder valve 13 and thus sealing the powder communication from between the reservoir hopper 1 and feed hopper 20, and at the same time sealing the gas flow passage 18. This sealing occurs before the filling plug 7 is completely removed and thus when the hopper 1 is opened, it is already powder and gas sealed from the remainder of the system. The remainder of the system continues to function in its normal manner with the powder feed occurring from the powder supply in the feed hopper 20, and the gas pressure equalization occurring through the equalizer tube 45, and connecting parts. After the reservoir hopper 1 has been refilled, the filling plug 7 is rescre-wed in place. As soon as the O-ring 9 is in position, a gas-tight seal is assured. As the filling plug 7 is further screwed down, it presses on the rod 14, opening the valve 13, allowing powder communication from the reservoir hopper 1 through the opening 12 into the feed hopper 20. Gas pressure equalization is furthermore reestablished through the passages 18, 17, hollow tube 4, and lateral passages 19. The exit end of the passages 18 are so positioned that gas flowing therethrough flows over the upper free surface of the powder in the feed hopper 20. A free powder surface is always established in the feed hopper 20 as the powder passing through the opening 12 will form a powder pile or heap with an upper surface having a conical shape as established by the natural angle of repose of the powder and once the apex of this cone fills the opening 12, further powder cannot pass from the reservoir hopper 1 to the feed hopper 20 until further powder is moved from the feed hopper 20. The exit of the passage 18 is so positioned that the gas flowing therethrough will pass over this free surface forcing a channel if neccessary, and thus preventing a clogging or blocking of the passage by the powder in the feed hopper 20.

It it is not necessary to refill the device during operation, the valve structure which seals the upper reservoir hopper from the lower hopper may be dispensed with. It is also possible to simply enlarge the feed hopper and to dispense with the entire reservoir hopper 1, constructing the plug 10 as a removable cover.

The pressure gauge 52 indicates the pressure of the carrier gas as it enters the mixing chamber 39 and thus indicates the pressure drop which occurs over the entire carrier gas conduit including its outlet orifice. In accordance with the invention the pressure drop along any segment or portion of the carrier gas conduit down stream of the point of introduction of the powder may be used for this indication. Thus, in place of the connection of the pressure gauge 52 as shown, a differential pressure gauge may be connected along any portion of the length of the carrier gas conduit past the point of powder introduction and the most accurate indication may be achieved by connecting the indicator across a given segment of the carrier gas tube or conduit past the fitting 51. Thus, for example, a manometer may be connected in this carrier gas conduit or tube with the two ends in communication at a spaced interval apart. This manometer will thus indicate a pressure drop along the conduit between its points of connection which constitutes a very accurate indication of the actual rate of powder flow, as for example, in quantity by weight, per unit of time, as for example, pounds per hour. It is possible to calibrate the gauge 52 or the manometer for a given powder so as to directly read the powder feed rate. This indication of the powder feed rate in accordance with the invention is, of course, not only applicable in connection with the type of powder feeder shown, but is applicable to any powder feeder system in which the powder is conveyed in a carrier gas which is flowing at a constant rate. By constant rate is meant a constant quantity of gas per unit time under the operating conditions as is conventionally measured by a flow meter, as for example a float-type flow meter.

The change in pressure drop dependent on the rate at which the powder is actually being conveyed, may be utilized in accordance with a further embodiment of the invention to automatically control the powder feed rate.

In the embodiment as shown in FIG. 7, a diaphragm chamber 56 with the flexible diaphragm 57 is connected so that the upper side of the diaphragm is in pressure communication by means of the tube 58 with the carrier gas in the mixing chamber 39 by T connection to the equalizer tube 45 and the lower side of the diaphragm is in pressure communication through the tube 59 with a portion of the carrier gas conduit 60 intermediate the connection 51 and flame spray gun, such as plasma type gun 61. The diaphragm 57 will thus move in responsive to changes in the pressure drop along this length of the conduit 60 between the mixing chamber 39 and in connection with 59. The diaphragm 57 actuates a movable contact 62 on the rheostat 63, through which the positive current connection from the motor 53 extends. As a greater quantity of the powder is fed through the conduit 60 the pressure differential across the diaphragm 57 will increase and the diaphragm 57 will be flexed downwardly moving the contact 62 downwardly and increasing the resistance, slowing the motor 53 down and decreasing the amount of powder fed by the bucket wheel 36. With the decrease in the powder feed, the reverse will occur. The rheostat actuated by the diaphragm thus provides an accurate control of the power-feed which operates on a feed-back system as the rate of the powder-feed itself controls the system. This change in pressure differential as caused by the rate of powder-feed may be utilized in any other known or conventional manner to control the amount of powder fed into the carrier gas and thus the pressure actuation may operate any electrical, electronic or mechanical device or valving arrangement for varying the feed of powder into the gas stream.

The change in pressure as caused by the quantity of powder being conveyed may also be directly used to regulate the quantity of powder fed by, for example, providing a device which must operate against the back pressure of the carrier gas in the conduit and in connection with which the feed rate decreases with an increase ing back pressure.

Such a device is diagrammatically shown in FIG. 8. This device corresponds to the powder feeding arrangement as shown in FIG. 1, except that the bucket wheel 36 is removed so that the powder simply forms a .pile 64 in the chamber 35. Due to the height of the point 40 as mentioned in connection with FIG. 1, the powder can not flow by gravity flow into the mixing chamber 39. A gas line 65 leads into the chamber 35 and terminates as a nozzle 66 below the surface 64 directed at the opening above the point 40 leading into the mixing chamber 39. A small quantity of gas is fed at a constant preset pressure set on the pressure regulator 66a. The gas emerging from the nozzle 66 will blow a quantity of the powder from the surface 64 into the mixing chamber 39 where the same is mixed with the carrier gas and flows out through the fitting 51 and conduit 60 in the manner previously described. The gas stream emerging from the nozzle 66 must operate against the back pressure in the line 60 as caused by the pressure drop and thus the quantity of the gas emerging from nozzle 66 will increase as the back pressure decreases, and decrease as the back pressure increases. The amount of powder blown into the mixing chamber 39 will depend on the gas flow through the nozzle 66. Thus, as a greater quantity of powder is blown into the mixing chamber 39'and conveyed through the conduit 60, the back pres sure will increase and thus the quantity of conveying gas passing through the nozzle 66 will correspondingly decrease, decreasing the amount of powder blown into the mixing chamber 39.

With a decrease in powder being conveyed through the conduit 60' the converse will occur so that the system is self-regulating, the regulation based on a feed-back principle, and the amount of powder fed is varied with variations in the pressure drop along the carrier gas conduit past the point of powder introduction.

This back pressure principle may be utilized in many other ways and manners to efiect the powder feed or the constant pressure gas operating against the carrier gas back pressure may be used to drive a mechanical powder feed device or for electrical control of such feed device, or for control valve actuation directly or indirectly.

While the invention has been described in detail with reference to certain specific embodiments, various changes and modificationswhich fall within the spirit of the invention will become apparent to the skilled artisan. The invention is therefore only intended to be limited by the appended claims or their equivalent wherein I have endeavored to claim all inherent novelty.

I claim:

1. In combination with a powder-feed device for a flame-spray gun having a mechanically driven powder conveyor introducing powder to be sprayed into a carrier gas flowing at a substantially constant rate through a conduit, a control system for controlling the powder flow rate comprising means responsive to change in pressure drop along the conduit past the point of powder introduction and means for varying the speed of said mechanically driven powder conveyor controlled by said pressure-sensitive means.

2. A powder feeder for a flame spray gun comprising a vertically extending powder feed chamber, a mixing chamber laterally spaced apart from said feed chamber, a bucket wheel chamber positioned between said feedand mixing chambers intersecting both chambers, the lowest point of intersection between said bucket wheel chamber and mixing chamber being of suflicient height to prevent gravity flow of powder from said feed chamber into said mixing chamber, a bucket wheel rotatably mounted in said bucket wheel chamber for conveying powder upon rotation from said feed chamber into said mixing chamber, means for maintaining said feed chamber filled with powder, means for rotating said bucket wheel at a controlled speed, and means for passing a carrier gas through said mixing chamber for entraining and carrying away powder fed by said bucket wheel for passage through a conduit to a flame spray gun.

3. Powder feeder according to claim 2 in which said bucket wheel chamber intersects said mixing chamber at a point lower than the axis of rotation of said bucket wheel and intersects said feed chamber at a point higher than the axis of rotation of said bucket wheel.

4. Powder feeder according to claim 2 including communicating gas passages to maintain said mixing and feed chambers at the same pressure.

5. Powder feeder according to claim 4 in which said means for maintaining said feed chamber filled with powder includes an enclosed substantially pressure-tight gravity feed hopper positioned above said feed chamber in gravity flow communication therewith and including a gas conduit pressure communicating said hopper with said mixing chamber for equalizing the pressure in said hopper with the mixing chamber pressure.

6. Powder feeder according to claim 5 including a pressure-tight reservoir hopper positioned above said feed hopper in gravity flow communication therewith and including a gas passage pressure communicating said feed hopper with the upper portion of said reservoir hopper, said reservoir hopper having a filling opening provided with a closure, and valve means actuated by removal of said closure for sealing said reservoir hopper from powder flow and pressure communication with said feed hopper.

7. Powder feeder according to claim 2 in which said feed chamber has a reverse taper at its upper portion, said bucket wheel chamber comprising a cylindrical chamber having a horizontal axis, said mixing chamber comprising a substantially vertically extending passage having a carrier gas nozzle at its upper end, the upper edge of the point of intersection of said feed and bucket wheel chambers being spaced above the lower edge of the point of intersection of the bucket wheel chamber and the mixing chamber at an angle of inclination of less than the natural angle of repose of powder to be fed through the gun, a pressure-tight gravity feed hopper mounted above in gravity flow communication with said feed chamber, a pressure equalizing gas line connecting the inlet to mixing chamber with the interior of said feed hopper and a gas equalization passage connecting the upper portion of said bucket wheel and feed chambers.

8. Powder feeder according to claim 7 in which said bucket wheel has a multiple number of bucket cutouts distributed about its periphery, is rotated about a substantially horizontal axis, and in which said means for rotating said bucket wheel is a variable speed electric motor, said mixing chamber having an outlet at its lower end leading into a horizontally extending accumulating chamber of increased cross-sectional inlet area conically narrowing to its outlet.

9. Powder feeder according to, claim 1, including a pressure gauge connected to respond to a change in pressure drop along the'conduit past the point of powder introduction for indicating the rate of powder feed.

10. Powder feeder according to claim 9 including a pressure actuated speed control device connected to said electric motor and actuated by the change in back pressure of the gas passing through said mixing chamber.

11, Powder feeder according to claim 2 including a pressure-sensitive gauge responsive to change in pressure drop along the conduit leading to the flame spray gun.

12. Powder feeder according to claim 2 including pressure-sensitive means responsive to change in pressure drop along said conduit leading to the flame spray gun, and means for varying the speed of rotation of said bucket wheel controlled by said pressure-sensitive means.

13. Powder feeder according to claim 12 in which said means for rotating said bucket wheel includes an electric motor and said means responsive to change in pressure drop includes a diaphragm in a diaphragm chamber connected for actuation of a speed control device for said electric motor.

14. Powder feeder according to claim 2 in which said conduit leading to the flame spray gun includes a horizontal accumulator chamber progressively decreasing in its cross-sectional area from its inlet to its outlet.

15. In combination with a powder-feed device for a flame spray gun having means for introducing powder to be sprayed into a carrier gas flowing at a substantially constant rate through a conduit, a control system for controlling the powder flow rate comprising means responsive to change in pressure drop along the conduit past the point of powder introduction and means for varying the rate at which powder is introduced into said carrier gas stream controlled by said pressure-sensitive means, said means for introducing powder including means for passing a feed gas at a constant pressure in contact with the powder to transport the same into the carrier gas stream whereby the flow rate of the feed gas varies with a change in pressure drop of the carrier gas thus varying the rate at which powder is introduced into the carrier gas stream.

16. Combination according to claim 15 in which said means for introducing powder includes a chamber, means for maintaining a pile of powder in said chamber, a feed gas conduit leading into said chamber and terminating as an outlet nozzle directed to blow powder from said pile into said carrier gas stream.

References Cited UNITED STATES PATENTS 885,069 4/1908 Mullikin 30242 2,200,713 5/1940 Ericson et a1. 222194 X 2,826,459 3/1958 Oetiker 30235 3,260,408 7/1966 Smitzer et al 222-194 X 2,549,736 4/1951 Wiese 239 2,726,118 12/1955 Jones et al. 23985 2,900,138 8/1959 Strate 23985 X 3,138,298 6/1964 Siebein et al 239-85 X EVERETT W. KIRBY, Primary Examiner U.S. c1. X.R. 222 194, 302-45, 4;

'fg jg f UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,501,097 Dated March 1.7 1970 Inventor (s6 HORACE S DALEY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I" Column 1, lines 47-48, "particulary' should be --particularly--; column 1, line 60, after "powder" cancel --fed to the stream, heretofore it has not beenand insert --bei.ng conveyed in the carrier as stream. Thus,--; column 2, line 35, "350" should be --35 men mm 1.". m.

" -M col-lesion 0: Patents Attcstingoffim 

